This application is based on Japanese Patent Application No. 11-236292 (1999) filed Aug. 24, 1999, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a pressure generating apparatus comprising a tube pump for squeezing an elastic tube to generate pressure therein, a printing apparatus including this pressure generating apparatus, and a method for controlling this printing apparatus.
The present invention is applicable to general printing apparatuses, apparatuses such as copying machines, facsimile machines having a communication system, and word processors having a printing section, as well as industrial printing apparatuses combined with various processing apparatuses in a compound manner.
2. Description of the Related Art
Printing apparatuses include those having functions of printers, copying machines, facsimile machines, or the like, or those used as output equipment for compound electronic equipment including a computer or a word processor or for work stations. These printing apparatuses are configured to images on printing media such as paper or thin plastic sheets.
Of these printing apparatuses, an ink jet type (ink jet printing apparatuses) carries out printing by ejecting ink onto a printing medium from a printing head acting as printing means. This ink jet printing apparatus has the advantages of allowing the printing head to be compactified easily, being able to print high-definition images at a high speed, being able to print images on plain paper without any special processing, and requiring reduced running costs. In addition, since this ink jet printing apparatus is based on the non-impact type, it makes reduced noise and can easily print color images using a large number of color inks. Alternatively, line type ink jet printing apparatuses using a line type printing head with a large number of nozzles arranged in a sheet width direction of printing paper can carry out printing at a higher speed.
In particular, ink jet type printing means (printing head) for using thermal energy to eject ink can be manufactured using a semiconductor fabrication process such as etching, deposition, or sputtering. Such printing means can further be compactified because liquid paths (nozzles) can be densely arranged therein by forming thermoelectric converters, electrodes, liquid path walls, roofs, or the like on a substrate.
The ink jet printing apparatus print an image on a printing medium by ejecting ink from the nozzles in response to electric signals. Entry of air into a nozzle or an increase in ink viscosity due to drying may preclude the nozzle from ejecting an ink droplet in response to electric signal. To recover the nozzle which cannot eject the ink properly, ink that does not contribute to image printing can be sucked and ejected from a tip of the nozzle (suction recovery). For this suction recovery means, a tube pump is often used as means for generating a negative pressure for sucking the ink. This tube pump generates a negative force inside a pump tube by rotating a pump roller in pressure contact with the pump tube, that is, squeezing the pump.
The suction recovery means comprises, for example, a cap that can cap the printing head and that has a suction port and an air communication port formed therein, the suction port being connected to a tube pump and the air communication port being connected to a valve rubber that is opened and closed by a valve lever. The cap and the tube pump are driven correlatively depending on a rotating direction of a PG motor, as shown, for example, by (a), (b), and (c) in FIG. 25. Additionally, the valve lever is driven depending on a rotating direction of a printing medium ejection roller rotated by an LF motor, as shown, for example, by (d) and (e) in FIG. 25.
First, the ejection roller is reversely driven for reverse rotation to cause the valve lever to open the valve rubber, and the PG motor subsequently rotates forward to bring the cap into abutment with a surface of the printing head which has the ink ejection port formed therein, to cap the printing head. At this point, the tube pump is forwardly driven for normal rotation due to the forward rotation (normal rotation) of the PG motor. The forward driving of the tube pump, however, prevents the pump roller from coming in pressure contact with the pump tube, so that the tube pump generates no negative force. Subsequently, the ejection roller is forwardly driven for normal rotation to cause the valve lever to close the valve rubber. Then, the PG motor rotates reversely to reversely drive the tube pump. When the tube pump is reversely driven for reverse rotation, the pump roller rotates in pressure contact with the pump tube to squeeze it to generate a negative force. This negative pressure is introduced into the cap through the suction port. Then, the cap caps the printing head and the air communication port is closed by the valve rubber, so that the negative pressure introduced into the cap causes ink of increased viscosity which is no longer suitable for printing as well as bubbles to be forcibly sucked and ejected from the ink ejection port of the printing head.
Subsequently, the ejection roller is reversely driven for reverse rotation to cause the valve lever to open the valve rubber. Then, the air communication port in the cap is opened to set the interior of the cap at atmospheric pressure. As a result, the ink is prevented from being sucked or ejected from the ink ejection port, while the ink inside the cap and the pump tube is sucked and ejected from an ink eject end of the pump tube (this operation is hereafter referred to as xe2x80x9cidle suctionxe2x80x9d). Subsequently, the PG motor is stopped, and the ejection roller is forwardly driven for normal rotation to separate the cap from the ink ejection port forming surface of the printing head to release the capping to cause the valve lever to close the valve rubber. Then, the series of suction recovery operations are completed.
The pressure generating apparatus in the conventional suction recovery means described above, however, has the following problems:
(1) In FIG. 25, reference t0 denotes a rotation start time when the pump roller of the tube pump starts rotating and reference t1 denotes a pressure generation time when the pump roller comes in complete pressure contact with the pump tube to start generating pressure. The amount of rotation made by the PG motor between a rotation start time P0 and the pressure generation time t1 varies depending on the position of the pump roller at the point of rotation start time t0, that is, deviations in the initial positions of the pump roller. Consequently, pressure generated by the tube pump is unstable.
(2) The unstable pressure from the tube pump significantly varies the amount of ink sucked during the suction recovery operation.
(3) If detection means is provided to detect the initial position of the pump roller to take action based on results of the detection, the inclusion of the detection means increases costs for the entire apparatus.
It is an object of the present invention to stably generate pressure by appropriately determining a point of time when a pressurization member such as a pump roller starts squeezing an elastic tube, that is, a point of time when a tube pump starts to generate pressure. It is another object of the present invention to provide a pressure generating apparatus that does not increase costs, a printing apparatus including this pressure generating apparatus, and a method for controlling this printing apparatus.
In the first aspect of the present invention, there is provided a pressure generating apparatus including a tube pump for, when a pressurization member is moved in a predetermined direction, squeezing the tube with the pressurization member coming into pressure contact with an elastic tube, thereby generating in the tube a pressure to be introduced into a pressure introduction section, the apparatus comprising:
switching means for switching to a state where the pressure from the tube pump can or cannot be introduced into the pressure introduction section; and
control means for allowing the switching means to switch to the state where the pressure from the tube pump can be introduced into the pressure introduction section after the pressurization member has moved a predetermined amount in the predetermined direction.
In the second aspect of the present invention, there is provided a printing apparatus that can print an image on a printing medium using a printing head capable of ejecting inks and that includes recovery means for effecting pressure on the printing head to eject ink that does not contribute to printing, from the printing head, the apparatus comprising:
the pressure generating means as claimed in claim 1 as a supply source of the pressure that is introduced into the recovery means.
In the third aspect of the present invention, there is provided a method for controlling a printing apparatus that can print an image on a printing medium using a printing head capable of ejecting ink and that includes recovery means for effecting pressure to the printing head to eject ink that do not contribute to printing, from the printing head, wherein:
a tube pump is provided as a supply source of pressure that is introduced into the recovery means,
when a pressurization member is moved in a predetermined direction, the tube pump squeezes the tube with the pressurization member coming into pressure contact with an elastic tube, thereby generating in the tube a pressure to be introduced into the recovery means,
after the pressurization member has moved a predetermined amount in the predetermined direction, a state is switched to one where the pressure from the tube pump can be introduced into the recovery means, from another where the pressure from the tube pump cannot be introduced into the recovery means.
The present invention comprises a tube pump including a pressurization member such as a pump roller that comes in pressure contact with an elastic tube and then squeezes it to generate pressure therein, wherein after the pressurization member has moved a predetermined amount, switching means switches to a state where the pressure from the tube pump can be introduced into a pressure introduction section. This allows adequate determination of a point of time when the pressurization member starts to squeeze the tube, that is, a point of time when the tube pump starts to generate pressure. As a result, the tube pump stably generates pressure, and an appropriate pressure can be introduced into the pressure introduction section such as a cap for a printing head of a printing apparatus to reliably provide an intended function such as ink suction recovery.
In addition, when the switching means switches to the state where the pressure from the tube pump can be introduced into the pressure introduction section, the movement of the pressurization member is temporarily stopped. Accordingly, after the operation of the switching means, the tube pump can be redriven to generate a stable pressure irrespective of variations in the amount of time required for the switching means to operate.
Additionally, a stable pressure can be generated without detection means for detecting the position of the pressurization member such as the pump roller. Accordingly, the absence of the detection means serves to reduce the costs of the apparatus.
The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.